This disclosure relates to releasable attachment devices of the type used to fasten, retain, or latch together components of an apparatus or a structure that are to be separated or released under controlled conditions.
Hook and loop type separable fasteners are well known and are used to join two members detachably to each other. These types of fasteners generally have two components disposed on opposing member surfaces. One component typically includes a plurality of resilient hooks while the other component typically includes a plurality of loops. When the two components are pressed together they interlock to form a releasable engagement. The resulting joint created by the engagement is relatively resistant to shear and pull forces, and weak in peel strength forces. As such, peeling one component from the other component can be used to separate the components with a minimal applied force. As used herein, the term xe2x80x9cshearxe2x80x9d refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to slide relatively to each other in a direction parallel to their plane of contact. The term xe2x80x9cpull forcexe2x80x9d refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to move relative to each other in a direction perpendicular to their plane of contact.
Magnetorheological (MR) fluids and elastomers are known as xe2x80x9csmartxe2x80x9d materials whose rheological properties can rapidly change upon application of a magnetic field. MR fluids are suspensions of micrometer-sized, magnetically polarizable particles in oil or other liquids. When a MR fluid is exposed to a magnetic field, the normally randomly oriented particles form chains of particles in the direction of the magnetic field lines (FIG. 1). The particle chains increase the apparent viscosity (flow resistance) of the fluid. The stiffness of the structure is accomplished by changing the shear and compression/tension moduli of the MR fluid by varying the strength of the applied magnetic field. The MR fluids typically develop structure when exposed to a magnetic field in as little as a few milliseconds. Discontinuing the exposure of the MR fluid to the magnetic field reverses the process and the fluid returns to a lower viscosity state. MR fluids enclosed in structural elements have been disclosed in U.S. Pat. No. 5,547,049.
Disclosed herein is a releasable fastener system that provides for a controlled release or separation of a joint in a shear and/or pull-off direction. A releasable fastener system comprises a loop portion comprising a support and a loop material disposed on a surface thereon; a hook portion comprising a support and a plurality of hook elements disposed on a surface, wherein the plurality of hook elements comprise a material adapted to change a shape orientation of the hook elements upon receipt of a magnetic signal; and an activation device coupled to the plurality of hook elements, the activation device being operable to selectively provide the magnetic signal to the hook elements and effectuate a change in the shape orientation of the hook elements to reduce or increase a shear force and/or a pull-off force.
In one embodiment, a releasable fastener system comprises hook elements comprised from a magnetic material, a magnetorheological fluid, a magnetorheological elastomer, and the like.
A process for operating a releasable fastener system comprises contacting a loop portion to a hook portion to form a releasable engagement, wherein the loop portion comprises a support and a loop material disposed on a surface thereon, and wherein the hook portion comprises a support and a plurality of hook elements disposed on a surface, wherein the plurality of hook elements comprises a material adapted to change a shape orientation upon receipt of an magnetic signal; maintaining constant shear and pull-off forces in the releasable engagement; selectively introducing the magnetic signal to the hook elements, wherein the magnetic signal is effective to change a shape orientation; and reducing shear and/or pull off forces in the releasable engagement.
A hook portion for a releasable fastener system comprises a support and a plurality of hook elements disposed on a surface of the support, wherein the plurality of hook elements comprise a material adapted to change a shape orientation upon receipt of a magnetic signal.
The above described and other features are exemplified by the following figures and detailed description.